Modern film scanners typically employ a linear imaging device such as a charge-coupled-device (CCD) for scanning film images to generate digital signals representative of the image information. A linear charge coupled device (CCD) imager contains a linear array of light detecting sites (hereafter "imaging pixels") which accumulate charge depending on the light energy projected onto them. After some charge accumulation time, the charges in the light detecting imaging pixels are transferred to a charge shifting structure so that the charges may be shifted out of the CCD and measured by some means in order to form a representation of the image projected onto the CCD. There are a number of signals which control the operation of the imager: clock signals which cause the charge to be shifted out of the imager, a transfer signal which causes the charge from the imaging pixels to be transferred to the shift structure, and one or more signals which electronically control exposure.
Typically, the control signals for the imager will be generated by a programmable logic device (PLD) or an application specific integrated circuit (ASIC). A counter circuit with a decoder is used to indicate when the charge clocking and transfer signals should be operated during the scan line. A counter with a reload value is used for each exposure control. These structures consume significant resources within a PLD or ASIC. Additionally, since they are embedded in the PLD program or the design of the ASIC, the structures are either inflexible or flexibility is gained at the cost of increased complexity and more resources.
If it is desired to make a change in the timing of control signals to a CCD imager, and the timing is embedded in the design of a PLD or ASIC, then the PLD or ASIC component must be physically removed from the system and replaced with an updated component. If this change is required as a field upgrade, the costs to upgrade will be significant. Additionally, if the component is an ASIC, significant costs may be incurred in modifying the design. There is therefore a need for an alternative, less costly and more flexible manner of controlling linear imaging devices when the control events occur during a line and this invention satisfies this need.